[Plugin: NextGEN Gallery] Trouble with images 'falling'

HI all, i’m having a problem with images in my gallery. I’ve posted a few galleries to various pages but i’m having a problem when viewing the fullsize image. Once on the full size image if Use the next and previous arrows to go through the pictures, the pictures start to ‘move, or fall’ down the page and I need to keep scrolling. Am I doing something stupid? Using the latest version of NextGen and WP 3.0.1. THanks in advance for anyone who can help ??

Rob